Abstract:

A wound suture containing a solvatochromatic indicator that undergoes a
color change in the presence of bacteria often associated with surgical
site infection is provided. Such a color change provides a "real time"
indication of the onset of infection, which may alert medical staff to
apply an appropriate antimicrobial treatment (e.g., antibiotic) to the
patient (e.g., human or animal) before a more serious infection occurs.
The patient may also be able to accurately monitor the condition of a
wound after discharge from the hospital. Further, the lack of a color
change may provide the medical staff or patient with the assurance that
the area is generally free of infection and clean.

Claims:

1. A wound suture comprising at least one filament, wherein the filament
contains a solvatochromatic indicator that undergoes a detectable color
change in the presence of bacteria.

2. The wound suture of claim 1, wherein the indicator is zwitterionic.

3. The wound suture of claim 2, wherein the zwitterionic indicator
includes a merocyanine dye.

4. The wound suture of claim 3, wherein the merocyanine dye has the
following structure: ##STR00013##

5. The wound suture of claim 2, wherein the zwitterionic indicator
includes an N-phenolate betaine dye.

8. The wound suture of claim 1, wherein the filament has a multifilament
configuration.

9. The wound suture of claim 1, wherein the filament has a monofilament
configuration.

10. The wound suture of claim 1, wherein the indicator constitutes from
about 0.01 wt. % to about 5 wt. %, based on the dry weight of the
filament.

11. The wound suture of claim 1, wherein the indicator is coated on a
surface of the filament.

12. The wound suture of claim 1, wherein the filament is attached to a
needle.

13. A method for detecting the presence of bacteria at a surgical incision
site, the method comprising:passing a needled suture through tissue to
create a wound closure, the suture containing a solvatochromatic
indicator that undergoes a detectable color change in the presence of
bacteria; andthereafter, observing the suture for the color change.

14. The method of claim 13, wherein the indicator is zwitterionic.

15. The method of claim 14, wherein the zwitterionic indicator includes a
merocyanine dye.

16. The method of claim 14, wherein the zwitterionic indicator includes an
N-phenolate betaine dye.

[0002]The most common way of preventing infection is to administer
prophylactic antibiotic drugs. While generally effective, this strategy
has the unintended effect of breeding resistant strains of bacteria.
Rather than using routine prophylaxis, a better approach is to practice
good wound management, i.e., keep the area free from bacteria before,
during, and after surgery, and carefully monitor the site for infection
during healing. Normal monitoring methods include close observation of
the wound site for slow healing, signs of inflammation and pus, as well
as measuring the patient's temperature for signs of fever. Unfortunately,
many symptoms are only evident after the infection is already
established. Furthermore, after a patient is discharged from the
hospital, they become responsible for monitoring their own healthcare,
and the symptoms of infection may not be evident to the unskilled
patient.

[0003]In response to these problems, techniques have been developed for
detecting wound-specific microorganisms. One such technique is described,
for instance, U.S. Patent Application Publication No. 2005/0142622 to
Sanders, et al. The technique of Sanders, et al. involves contacting a
sample with a labeled substrate for an enzyme produced or secreted by a
microorganism, and thereafter detecting the modification of the
substrate. Unfortunately, however, such techniques are far too complex
for practical use. Instead, what is needed is a relatively simple and
effective technique for detecting the early stages of bacterial
infection.

SUMMARY OF THE INVENTION

[0004]In accordance with one embodiment of the present invention, a wound
suture is disclosed that comprises at least one filament. The filament
contains a solvatochromatic indicator that undergoes a detectable color
change in the presence of bacteria. In accordance with another embodiment
of the present invention, a method for detecting the presence of bacteria
at a surgical incision site is disclosed. The method comprises passing a
needled suture through tissue to create a wound closure, the suture
containing a solvatochromatic indicator that undergoes a detectable color
change in the presence of bacteria. Thereafter, the suture is observed
for the color change.

[0005]Other features and aspects of the present invention are discussed in
greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]A full and enabling disclosure of the present invention, including
the best mode thereof, directed to one of ordinary skill in the art, is
set forth more particularly in the remainder of the specification, which
makes reference to the appended figure in which:

[0007]FIG. 1 is a schematic illustration of one embodiment of a
suture-needle assembly that may be employed in the present invention.

[0008]Repeat use of reference characters in the present specification and
drawing is intended to represent same or analogous features or elements
of the invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

[0009]Reference now will be made in detail to various embodiments of the
invention, one or more examples of which are set forth below. Each
example is provided by way of explanation of the invention, not
limitation of the invention. In fact, it will be apparent to those
skilled in the art that various modifications and variations may be made
in the present invention without departing from the scope or spirit of
the invention. For instance, features illustrated or described as part of
one embodiment, may be used on another embodiment to yield a still
further embodiment. Thus, it is intended that the present invention
covers such modifications and variations as come within the scope of the
appended claims and their equivalents.

[0010]Generally speaking, the present invention is directed to a wound
suture containing a solvatochromatic indicator that undergoes a color
change in the presence of bacteria often associated with surgical site
infection, such as Streptococcus pyogenes (S. pyogenes), Pseudomonas
aeruginosa (P. aeruginosa), Enterococcus faecalis (E. faecalis), Proteus
mirabilis (P. mirabilis), Serratia marcescens (S. marcescens),
Enterobacter clocae (E. clocae), Acetinobacter anitratus (A. anitratus),
Klebsiella pneumoniae (K. pneumonia), Escherichia coli (E. coli),
Staphyloccus aureus (S. aureus), coagulase-negative Staphylococci,
Enterococcus spp., and so forth. Such a color change provides a "real
time" indication of the onset of infection, which may alert medical staff
to apply an appropriate antimicrobial treatment (e.g., antibiotic) to the
patient (e.g., human or animal) before a more serious infection occurs.
The patient may also be able to accurately monitor the condition of a
wound after discharge from the hospital. Further, the lack of a color
change may provide the medical staff or patient with the assurance that
the area is generally free of infection and clean.

[0011]Merocyanine indicators (e.g., mono-, di-, and tri-merocyanines) are
one example of a type of solvatochromatic indicator that may be employed
in the present invention. Merocyanine indicators, such as merocyanine
540, fall within the donor--simple acceptor indicator classification of
Griffiths as discussed in "Colour and Constitution of Organic Molecules"
Academic Press, London (1976). More specifically, merocyanine indicators
have a basic nucleus and acidic nucleus separated by a conjugated chain
having an even number of methine carbons. Such indicators possess a
carbonyl group that acts as an electron acceptor moiety. The electron
acceptor is conjugated to an electron donating group, such as a hydroxyl
or amino group. The merocyanine indicators may be cyclic or acyclic
(e.g., vinylalogous amides of cyclic merocyanine indicators). For
example, cyclic merocyanine indicators generally have the following
structure:

##STR00001##

[0012]wherein, n is any integer, including 0. As indicated above by the
general structures 1 and 1', merocyanine indicators typically have a
charge separated (i.e., "zwitterionic") resonance form. Zwitterionic
indicators are those that contain both positive and negative charges and
are net neutral, but highly charged. Without intending to be limited by
theory, it is believed that the zwitterionic form contributes
significantly to the ground state of the indicator. The color produced by
such indicators thus depends on the molecular polarity difference between
the ground and excited state of the indicator. One particular example of
a merocyanine indicator that has a ground state more polar than the
excited state is set forth below as structure 2.

##STR00002##

[0013]The charge-separated left hand canonical 2 is a major contributor to
the ground state whereas the right hand canonical 2' is a major
contributor to the first excited state. Still other examples of suitable
merocyanine indicators are set forth below in the following structures
3-13.

##STR00003## ##STR00004##

[0014]wherein, "R" is a group, such as methyl, alkyl, aryl, phenyl, etc.

[0015]Indigo is another example of a suitable solvatochromatic indicator
for use in the present invention. Indigo has a ground state that is
significantly less polar than the excited state. For example, indigo
generally has the following structure 14:

##STR00005##

[0016]The left hand canonical form 14 is a major contributor to the ground
state of the indicator, whereas the right hand canonical 14' is a major
contributor to the excited state.

[0017]Other suitable solvatochromatic indicators that may be used in the
present invention include those that possess a permanent zwitterionic
form. That is, these indicators have formal positive and negative charges
contained within a contiguous π-electron system. Contrary to the
merocyanine indicators referenced above, a neutral resonance structure
cannot be drawn for such permanent zwitterionic indicators. Exemplary
indicators of this class include N-phenolate betaine indicators, such as
those having the following general structure:

##STR00006##

[0018]wherein R1--R5 are independently selected from the group
consisting of hydrogen, a nitro group (e.g., nitrogen), a halogen, or a
linear, branched, or cyclic C1 to C20 group (e.g., alkyl,
phenyl, aryl, pyridinyl, etc.), which may be saturated or unsaturated and
unsubstituted or optionally substituted at the same or at different
carbon atoms with one, two or more halogen, nitro, cyano, hydroxy,
alkoxy, amino, phenyl, aryl, pyridinyl, or alkylamino groups. For
example, the N-phenolate betaine indicator may be
4-(2,4,6-triphenylpyridinium-1-yl)-2,6-diphenylphenolate (Reichardt's
dye) having the following general structure 15:

##STR00007##

[0019]Reichardt's dye shows strong negative solvatochromism and may thus
undergo a significant color change from blue to colorless in the presence
of bacteria. That is, Reichardt's dye displays a shift in absorbance to a
shorter wavelength and thus has visible color changes as solvent eluent
strength (polarity) increases. Still other examples of suitable
negatively solvatochromatic pyridinium N-phenolate betaine indicators are
set forth below in structures 16-23:

##STR00008##

[0020]wherein, R is hydrogen, --C(CH3)3, --CF3, or
C6F13.

##STR00009## ##STR00010##

[0021]Still additional examples of indicators having a permanent
zwitterionic form include indicators having the following general
structure 24:

##STR00011##

[0022]wherein, n is 0 or greater, and X is oxygen, carbon, nitrogen,
sulfur, etc. Particular examples of the permanent zwitterionic indicator
shown in structure 24 include the following structures 25-33.

[0024]Although the above-referenced indicators are classified as
solvatochromic, it should be understood that the present invention is not
necessarily limited to any particular mechanism for the color change of
the indicator. Even when a solvatochromic indicator is employed, other
mechanisms may actually be wholly or partially responsible for the color
change of the indicator. For example, acid-base or proton donation
reactions between the indicator and microbe may result in the color
change. As an example, highly organized acid moieties on bacteria cell
walls may protonate certain indicators, resulting in a loss of color.
Redox reactions between the indicator and microbe may likewise contribute
to the color change.

[0026]The construction of the wound suture may be monofilament or
multifilament, such as a bundle of individual filaments, a yarn or tow
(that may be entangled, twisted or plied) or filaments or yarns that have
been braided, knitted or woven. Suitable braided multifilament
constructions for sutures are described in U.S. Pat. Nos. 5,019,093;
5,059,213 and 4,959,069, which are incorporated herein in the entirety by
reference thereto for all purposes. Typically, at least one of the
filaments in a multifilament core is oriented so that a significant
number of the molecules within the fiber are positioned substantially
parallel to the length of the fiber to impart strength parallel to the
fibers length. The filaments are generally drawn at least 2 times their
original length to orient the molecules in the fibers. Still other known
suture constructions may be employed, such as surgical meshes (e.g.,
hernia repair mesh), brachy seed spacers, etc.

[0027]If desired, the indicator may be incorporated into the wound suture
during its formation. Alternatively, the indicator may be coated onto all
or only a portion of the wound suture. Suitable techniques for coating
the indicator onto the suture include printing, dipping, spraying, melt
extruding, coating (e.g., solvent coating, powder coating, brush coating,
etc.), and so forth. In one embodiment, for example, the wound suture is
dipped into a solution containing the indicator. Besides the indicator,
the solution may contain other components, such as a mobile carrier. The
carrier may be a liquid, gas, gel, etc., and may be selected to provide
the desired performance (time for change of color, contrast between
different areas, and sensitivity) of the indicator. In some embodiments,
for instance, the carrier may be an aqueous solvent, such as water, as
well as a non-aqueous solvent, such as glycols (e.g., propylene glycol,
butylene glycol, triethylene glycol, hexylene glycol, polyethylene
glycols, ethoxydiglycol, and dipropyleneglycol); alcohols (e.g.,
methanol, ethanol, n-propanol, and isopropanol); triglycerides; ethyl
acetate; acetone; triacetin; acetonitrile, tetrahydrafuran; xylenes;
formaldehydes (e.g., dimethylformamide, "DMF"); etc. Upon application,
the solution may be dried to remove the carrier and leave a residue of
the indicator for interacting with a microorganism.

[0028]Other additives may also be employed, either separately or in
conjunction with the indicator. In one embodiment, for instance,
cyclodextrins are employed that enhance the sensitivity and contrast of
an indicator. While not wishing to be bound by theory, such additives may
inhibit the crystallization of the indicator and thus provide a more
vivid color and also enhance detection sensitivity. That is, single
indicator molecules have greater sensitivity for microorganisms because
each indicator molecule is free to interact with the microbial membrane.
In contrast, small crystals of indicator have to first dissolve and then
penetrate the membrane. Examples of suitable cyclodextrins may include,
but are not limited to, hydroxypropyl-β-cyclodextrin,
hydroxyethyl-β-cyclodextrin, γ-cyclodextrin,
hydroxypropyl-γ-cyclodextrin, and
hydroxyethyl-γ-cyclodextrin, which are commercially available from
Cerestar International of Hammond, Ind.

[0031]The exact quantity of the indicator employed in the present
invention may vary based on a variety of factors, including the
sensitivity of the indicator, the presence of other additives, the
desired degree of detectability (e.g., with an unaided eye), the
suspected concentration of the microorganism, etc. In some cases, it is
desirable to only detect the presence of bacteria at a pathogenic
concentration. For example, a bacterial concentration of about
1×103 colony forming units ("CFU") per milliliter of growth
media or more, in some embodiments about 1×105 CFU/ml or more,
in some embodiments about 1×106 CFU/ml or more, and in some
embodiments, about 1×107 CFU/ml or more may be considered
pathogenic. It should be understood that such concentrations may
correlate to a liquid sample or a non-liquid sample (e.g., skin or
obtained from skin) that is cultured in a growth media. Regardless, the
indicator may be employed in an amount sufficient to undergo a detectable
color change in the presence of bacteria at a desired concentration. For
instance, the indicator may be present in a solution in an amount from
about 1 wt. % to about 50 wt. %, in some embodiments from about 5 wt. %
to about 40 wt. %, and in some embodiments, from about 10 wt. % to about
35 wt. %. Upon application, the indicator may constitute from about 0.01
wt. % to about 5 wt. %, in some embodiments from about 0.05 wt. % to
about 3 wt. %, and in some embodiments from about 0.1 wt. % to about 1
wt. %, based on the dry weight of the wound suture.

[0032]During a surgical procedure, the wound suture is typically attached
to a needle as is well known in the art. Referring to FIG. 1, for
example, a suture needle combination 10 is illustrated that contains a
suture 11 attached to a surgical needle 17 using any conventional swaging
technique. A user may grasp the needle 17 using an appropriate surgical
instrument and penetrate bodily tissue at or near an incisional wound.
The needle 17 may then be passed through the tissue until it penetrates
the other side of the incisional wound. Once the needle 17 is passed
through both sides of the incisional site, it may be pulled away from the
tissue until the slip knot contacts the tissue at the point of entry of
the needle. At this point, the needle 17 may be passed through each of
the loops and knotted as is known in the art.

[0033]During or after closure of the wound with the suture, the presence
of bacteria at the wound site may be readily detected by observing
(either visually or with instrumentation) the color change. This allows
detection of infection directly within the wound site, on the dermis and
subcutaneous area of a wound site, or in exudates seeping from the suture
holes and/or when the suture is removed. The color change may be rapid
and may be detected within a relatively short period of time. For
example, the change may occur in about 5 minutes or less, in some
embodiments about 1 minute or less, in some embodiments about 30 seconds
or less, in some embodiments about 20 seconds or less, and in some
embodiments, from about 10 seconds to about 2 minutes. Conversely, the
color change could be used to monitor the build up of microbial
contamination on the skin surface over time. The microbes could be
already present, in the or on the skin, in very small amounts and with
time multiply to form a colony with sufficient number that a serious
infection would result. They could also come from contamination after
surgery through contact with infected hands, instruments or needles etc.
Thus, the color change may indicate an instant contamination of a high
number of microbes present or the build-up of microbes on or in the skin
over time.

[0034]Regardless of when it occurs, the extent of the color change may be
determined either visually or using instrumentation (e.g., optical
reader) and provide a "real-time" indication of infection at a wound or
incision site. The extent of the color change may be represented by a
certain change in the absorbance reading as measured using a conventional
test known as "CIELAB", which is discussed in Pocket Guide to Digital
Printing by F. Cost, Delmar Publishers, Albany, N.Y. ISBN 0-8273-7592-1
at pages 144 and 145. This method defines three variables, L*, a*, and
b*, which correspond to three characteristics of a perceived color based
on the opponent theory of color perception. The three variables have the
following meaning:

[0035]L*=Lightness (or luminosity), ranging from 0 to 100, where 0=dark
and 100=light;

[0036]a*=Red/green axis, ranging approximately from -100 to 100; positive
values are reddish and negative values are greenish; and

[0037]b*=Yellow/blue axis, ranging approximately from -100 to 100;
positive values are yellowish and negative values are bluish.

[0038]Because CIELAB color space is somewhat visually uniform, a single
number may be calculated that represents the difference between two
colors as perceived by a human. This difference is termed ΔE and
calculated by taking the square root of the sum of the squares of the
three differences (ΔL*, Δa*, and Δb*) between the two
colors. In CIELAB color space, each ΔE unit is approximately equal
to a "just noticeable" difference between two colors. CIELAB is therefore
a good measure for an objective device-independent color specification
system that may be used as a reference color space for the purpose of
color management and expression of changes in color. Using this test,
color intensities (L*, a*, and b*) may thus be measured using, for
instance, a handheld spectrophotometer from Minolta Co. Ltd. of Osaka,
Japan (Model # CM2600d). This instrument utilizes the D/8 geometry
conforming to CIE No. 15, ISO 7724/1, ASTME1164 and JIS Z8722-1982
(diffused illumination/8-degree viewing system. The D65 light reflected
by the specimen surface at an angle of 8 degrees to the normal of the
surface is received by the specimen-measuring optical system. Typically,
the indicator undergoes a color change that is represented by a ΔE
of about 2 or more, in some embodiments about 3 or more, and in some
embodiments, from about 5 to about 50.

[0039]The present invention may be better understood with reference to the
following examples.

EXAMPLE 1

[0040]The following braided sutures were employed in this example: coated
VICRYL (Ethicon, Inc.), which is made from Polyglactin 910
(poly(glycolide-co-trimethylene carbonate)) and has a length of 27
inches; POLYSORB (US Surgical Corp.), which is made from lactomer 9-1
(poly(lactide-co-glycolide) and has a length of 18 inches; and DEXON "S"
beige (Sherwood Davis & Geck), which is made from polyglycolic acid TT-20
and has a length of 18 inches. Each of the braided sutures was soaked in
an acetontrile solution containing Reichardt's dye (20% wt/wt) overnight
at ambient temperature in a sealed container. The sutures were then
removed and placed on a glass plate and allowed to air dry in a fumehood
over the weekend. The dried sutures had a blue purple color. This coating
was not removed when rubbed with a dry paper towel.

EXAMPLE 2

[0041]The following monofilament sutures were employed in this example:
coated MONOCRYL (Ethicon, Inc.), which is made from poliglecaprone 25 (a
copolymer of glycolide and ε-caprolactone) and has a length of 27
inches; CHROMIC GUT (Ethicon, Inc.), which is made primarily from
collagen and has a length of 27 inches; BIOSYN (US Surgical Corp.), which
is made from (glycomer 631, poly(dioxanone)-polyglycolide-trimethylene
carbonate) and has a length of 36 inches; and PLAIN GUT (US Surgical),
which is made primarily from collagen and has a length of 30 inches. Each
of the monofilament sutures was soaked in an acetontrile solution
containing Reichardt's dye (20% wt/wt) overnight at ambient temperature
in a sealed container. The sutures were then removed and placed on a
glass plate and allowed to air dry in a fumehood over the weekend. The
monofilament sutures had a purple color, although not as deep a color as
the braided filament sutures of Example 1.

EXAMPLE 3

[0042]Examples 1 and 2 were repeated with an isopropanol solution of
Reichardt's dye (12% wt/wt).

EXAMPLE 4

[0043]Four (4) turkey thighs (Kroger grocery store) were slit with a
scalpel to make several 3'' long incisions. These wounds were then sewn
up using the dye-coated sutures of Example 1 (coated VICRYL and POLYSORB)
and Example 2 (MONOCRYL). The sutures had needles attached to the suture
and a herring bone pattern technique was used. The wound site area with
the sutures was treated with a suspension of 1×105 CFU (colony
forming units) of S. aureus and the color of the sutures observed. Within
seconds, the purple color of the sutures was discharged to colorless
where the sutures had contacted the S. aureus.

EXAMPLE 5

[0044]Eight (8) chicken legs (Kroger grocery store) were slit with a
scalpel to make several 3'' long incisions. These wounds were then sewn
up using the dye-coated sutures of Example 1 (DEXON "S" beige and
POLYSORB) and Example 2 (BIOSYN). The sutures had needles attached to the
suture and a herring bone pattern technique was used. The wound site area
with the sutures was treated with a suspension of 1×105 CFU
(colony forming units) of S. aureus and the color of the sutures
observed. Within seconds, the purple color of the sutures was discharged
to colorless where the sutures had contacted the S. aureus.

EXAMPLE 6

[0045]A turkey thigh and chicken leg from Example 4 (POLYSORB) was placed
into sealable bags and left at ambient temperature overnight. Another
chicken leg from Example 5 (DEXON "S" beige ) was also placed in a
sealable bag and placed in a refrigerator overnight. After 10 hours, the
thigh and legs at ambient temperature were observed and the sutures had
turned colorless, thereby indicating that it had spoiled. The
refrigerated chicken leg, however, had no discharge of the suture coating
color, thereby indicating that it had not spoiled.

[0046]While the invention has been described in detail with respect to the
specific embodiments thereof, it will be appreciated that those skilled
in the art, upon attaining an understanding of the foregoing, may readily
conceive of alterations to, variations of, and equivalents to these
embodiments. Accordingly, the scope of the present invention should be
assessed as that of the appended claims and any equivalents thereto.